Additive manufacturing using foaming radiation-curable resin

ABSTRACT

SLA-based additive manufacturing using radiation-curable foams enables the production by 3D printing of lightweight parts having desirable physical and functional attributes. A representative method of manufacturing such items includes processing a radiation-curable resin in liquid form to produce a stable, non-aqueous radiation-curable foam, on-demand deposition of the foam at a build layer of a build surface within a 3D printer, and then curing the non-aqueous radiation-curable foam to produce a layer of a 3D build item. Processing the resin typically includes agitation, mixing, shaking, gas injection, ultrasonic stimulation, or combinations thereof. 3D articles of manufacture made by the above-described manufacturing process are also provided.

BACKGROUND Technical Field

This application relates generally to additive manufacturing techniques.

Brief Description of the Related Art

Stereolithography (SLA) is a form of three-dimensional (3D) printingtechnology used for creating models, prototypes, patterns and productionparts in a layer by layer fashion (so-called “additive manufacturing”)using photo-polymerization, a process by which light causes chains ofmolecules to link, forming polymers. Those polymers then make up thebody of a three-dimensional solid. Typically, an SLA additivemanufacturing process uses a build platform having a build traysubmerged in a liquid photosensitive material. A 3D model of the item tobe manufactured is imported into an associated 3D printer software,which software slices the 3D model into 2D images that are thenprojected onto the build platform to expose the photopolymer.

SLA additive manufacturing has the potential to revolutionize themanufacturing industry. Its high resolution and broad range ofchemistries allow the production of complex shapes and structures with avariety of characteristics that range from rigid to very flexible, hightemperature-stable, and investment casting resins. Further, while thesetechniques have proven to produce satisfactory results, they havecertain limitations that have prevented their widespread use for generalmanufacturing. Foremost, additive manufacturing technologies are slowand only produce small parts. As a result, they are used predominatelyfor prototyping parts and not manufacturing. In particular, slowproduction speeds, which are by a plurality of technical limitations,make SLA additive manufacturing suitable only for rapid prototyping (orsmall quantity production at best), and it produces parts that are of asub-meter scale in size. These issues currently prevent SLA fromdisrupting traditional manufacturing beyond rapid prototyping.

In particular, current SLA build volumes typically are less than twelvesquare inches. One approach to address this limitation is described, forexample, in U.S. Publication No. 2017/0100885, assigned to Carbon, Inc.d/b/a Carbon3D, which publication describes the use of a plurality oftiled projectors for making larger build volumes, e.g., up to five (5)square meters, in part by what the publication describes as (i)continuously maintaining a dead zone of polymerizable liquid in contactwith a build surface, and (ii) continuously maintaining a gradient ofpolymerization zone (an active surface on the bottom of a growing threedimensional object) between the dead zone and the solid polymer and incontact with each thereof, the gradient of polymerization zonecomprising the polymerizable liquid in partially cured form. Thistechnique (e.g., exploiting the oxygen permeable deadzone withhyper-oxygen-permeable amorphous teflon coatings), however, lackscommercial feasibility. In particular, the cost of such materials isapproximately $5,000 per square foot. Therefore, a five meter square (54square foot) build plate would require $270,000 of amorphous teflon.While not out of scope for some industrial equipment capital costs, thisis a significant expense. Further, at this scale build windows are knownto cloud with time due to the interaction of the UV blocker with thetransparent surface chemistry. As such, this would be an expensivedisposable component. Another potential issue with scaling thistechnology is the amount of resin that is required. The retail price ofresin is between $120 and $250 per liter. For every 2.54 cm (1 inch) ofdepth, a five meter square build volume would require 127 liters to fillthe tank. Assuming the underlying materials are on the order of$20-$40/L, this would cost $5,000 to charge, plus replacing whateverresin is required to produce the parts to keep the level at steadystate.

Still another issue with SLA production at larger scales is that thephotochemical reaction and subsequent polymerization is exothermic,which produces excess heat as a reaction by-product. Further, subsequentcuring of finished parts are known to shrink by 40% for free radicalinitiated chemistries, but only about 4% for cationic chemistries.

Given the known limitations and deficiencies in the prior art, anunfilled need exists for larger area additive manufacturing thatproduces high quality surfaces that do not require extensive postprocessing, that can be manufactured at reasonable speeds, and that canbe commercialized in an otherwise cost-effective way.

The technique and approach of this disclosure addresses this long-feltneed.

BRIEF SUMMARY

SLA-based additive manufacturing using radiation-curable foams enablesthe production by 3D printing of lightweight parts having desirablephysical and functional attributes. A representative method ofmanufacturing such items includes processing a radiation-curable resinin liquid form to produce a stable, non-aqueous radiation-curable foam,on-demand deposition of the foam at a build layer of a build surfacewithin a 3D printer, and then solidifying the non-aqueousradiation-curable foam to produce a layer of a 3D build item. Processingthe resin typically includes agitation, mixing, shaking, gas injection,ultrasonic stimulation, or combinations thereof. 3D articles ofmanufacture made by the above-described manufacturing process are alsodescribed.

The foregoing has outlined some of the more pertinent features of thesubject matter. These features should be construed to be merelyillustrative. Many other beneficial results can be attained by applyingthe disclosed subject matter in a different manner or by modifying thesubject matter as will be described.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the subject matter and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a known prior art “top-down” 3D printer implementationenvironment in which the techniques of this disclosure may be practiced;

FIG. 2 is a known prior art “bottom-up” implementation environment inwhich the techniques of this disclosure may be practiced;

FIG. 3 depicts how the techniques of this disclosure may be implementedby retrofitting an existing printer to accommodate foam-based printingaccording to this disclosure;

FIG. 4 depicts a cross-section of a control sample printed in aconventional manner using a liquid resin;

FIG. 5 depicts a cross-section of a sample (shown under ring light)printed using foam according to the technique of this disclosure;

FIG. 6 depicts a cross-section of the foam-printed sample (shown underconfocal light); and

FIG. 7 depicts a chart that, for each of a set of layer sizes tested,compares relative percentages of gas and solid volume fractions in theresulting samples.

DETAILED DESCRIPTION

As previously described, stereolithography is a known technique formaking solid objects by successively “printing” thin layers of a curablematerial, e.g., a radiation-curable material, one on top of the other.To this end, a programmed movable spot beam of light (e.g., UV) shiningon a surface or layer of radiation-curable liquid is used to form asolid cross-section of the object at the surface of the liquid. As U.S.Pat. No. 4,575,330 teaches, the object is then moved, in a programmedmanner, away from the liquid surface by the thickness of one layer andthe next cross-section is then formed and adhered to the immediatelypreceding layer defining the object. This process is continued until theentire object is formed. Using this printing approach, many differenttypes of object forms can be created using the computer to help generatethe programmed commands and to then send the program signals to thestereolithographic object forming subsystem.

FIG. 1 depicts a known prior art “top-down” approach to printing. Thisfigure is reproduced from U.S. Pat. No. 4,575,330. Here, a container 21is filled with a UV curable liquid 22 or the like, to provide adesignated working surface 23. A programmable source of ultraviolet (UV)light 26 or the like produces a spot of ultraviolet light 27 in theplane of surface 23. The spot 27 is movable across the surface 23 by themotion of mirrors or other optical or mechanical elements that are apart of light source 26. The position of the spot 27 on surface 23 iscontrolled by a computer 28. A movable elevator platform 29 insidecontainer 21 is moved up and down selectively, the position of theplatform being controlled by the computer 28. The elevator platform maybe driven mechanically, pneumatically, hydraulically or electrically,and it typically uses optical or electronic feedback to preciselycontrol its position. As the device operates, it produces athree-dimensional object 30 by step-wise buildup of integrated laminaesuch as 30 a, 30 b, 30 c. During this operation, the surface of the UVcurable liquid 22 is maintained at a constant level in the container 21,and the spot of UV light 27 is moved across the working surface 23 in aprogrammed manner. As the liquid 22 cures and solid material forms, theelevator platform 29 that was initially just below surface 23 is moveddown from the surface in a programmed manner by any suitable actuator.In this way, the solid material that was initially formed is taken belowsurface 23 and new liquid 22 flows across the surface 23. A portion ofthis new liquid is, in turn, converted to solid material by theprogrammed UV light spot 27, and the new material adhesively connects tothe material below it. This process is continued until the entirethree-dimensional object 30 is formed.

A computer controlled pump (not shown) may be used to maintain aconstant level of the liquid 22 at the working surface 23. Appropriatelevel detection system and feedback networks can be used to drive afluid pump or a liquid displacement device to offset changes in fluidvolume and maintain constant fluid level at the surface 23.Alternatively, the source 26 can be moved relative to the sensed level23 and automatically maintain sharp focus at the working surface 23. Allof these alternatives can be readily achieved by conventional softwareoperating in conjunction with the computer control system 28.

An alternative approach is to build the item from the “bottom-up” asdepicted in FIG. 2, which is also reproduced from U.S. Pat. No.4,575,330. In this approach, the UV curable liquid 22 floats on aheavier UV transparent liquid 32 that is non-miscible and non-wettingwith the curable liquid 22. By way of example, ethylene glycol or heavywater are suitable for the intermediate liquid layer 32. In the systemof FIG. 2, the three-dimensional object 30 is pulled up from the liquid22, rather than down and further into the liquid medium, as shown in thesystem of FIG. 1. In particular, the UV light source 26 in FIG. 2focuses the spot 27 at the interface between the liquid 22 and thenon-miscible intermediate liquid layer 32, the UV radiation passingthrough a suitable UV transparent window 33, of quartz or the like,supported at the bottom of the container 21.

According to the techniques of this disclosure, and in lieu of printingjust from resin in its liquid phase, one or more layers of the item areprinted from resin that is foamed (at the build surface 23). In general,printing “foam” is highly desirable because, as compared to liquid, foamoccupies a same volume (e.g., the tank) with significantly less material(by mass) than the same amount of resin in liquid form. Thus, because atleast in part foamed resin is used to facilitate 3D manufacture of anitem, significant manufacturing costs and efficiencies are obtained asless material is required to produce the item. Experimental dataestablishing this principle is set forth below.

With the above as background, FIG. 3 depicts a representativeimplementation of an additive manufacturing method and apparatus of thisdisclosure wherein resin foam is the source material for the printer. Atop-down printing method is depicted although the techniques herein (ofprinting at a foam layer) may be implemented in a bottom-up manner aswell. In this example embodiment, the SLA apparatus comprises aradiation source 300 (e.g., DLP, laser, electron beam (EB), x-ray, etc.and scanner), a movement control mechanism 302 (e.g., a stepper motor)that moves a build platform 304 vertically up and down within a tank 305that holds the photopolymer resin 306, and a sweeper 308 (also known asa “recoater” blade) that sweeps horizontally. These elements are used toprint a part 310 in the manner previously described.

According to this disclosure, the SLA apparatus is augmented with a foamproducing and dispensing mechanism to facilitate production of resinfoam at the printer interface, namely, the layer being printed. To thisend, the mechanism comprises a foaming or pressure vessel 312, anelectromechanical valve 314, and a hose or tube 316. A manifold 318 isattached to the sweeper 308 to evenly distribute the foamed resin acrossthe top layer of the build surface. In particular, and as depicted, thefoaming vessel receives liquid resin and a suitable gas (e.g., CO₂, N₂O,etc.). Gas is dissolved in the liquid resin within the foaming vessel(e.g., by shaking, missing, agitation, etc.) and selectively deliveredto the build plate/platform via the hose 316 when the valve 314 isactuated, e.g., by a solenoid or other electromechanical, pneumatic,optical or electronic control device. Typically, the mechanism is underprogram control using a computer, which may be the same computer used tocontrol the printer. In this embodiment, the mechanism includes afrother 320 (e.g., a mechanical agitator, an ultrasonic device, etc.) toshake or otherwise dissolve the gas within the liquid vessel if neededto produce foam.

Upon delivery of the resin and gas mixture (directly onto the buildplate via the manifold 318), the gas spontaneously evolves out of theliquid mixture (due to the lower pressure) to produce a foam that isradiation-curable. The sweeper 308 spreads the foam evenly onto theplate, and the light engine is then activated to display the appropriateimage to cure (solidify) the foam into a layer. Once the layer isformed, the movement control mechanism moves the platform down so thatthe next layer of the item can be built; the process is then repeated,once again preferably using the foam layer at the print interface.

Preferably, the foam dispensing is carried out in an automated mannerand “on-demand” (meaning the foam is produced “just-in-time” tofacilitate the printing of the current layer while the foam remainsstable), once again under program control, so that the layer(s) arebuilt up in a continuous manner.

Conventionally, 3D printing comprises a start-up procedure by which the3D printer is prepared and internal states are set. Layer preparationand exposure is then initiated (under software program control),preferably using a deep dip (to recoat a top layer with excess resin),followed by conventional operations, namely: raise, recoat, range find,fine adjustment, exposure, and then repeat, followed eventually byshutdown. According to the approach herein, the above-described layerpreparation and exposure operations are modified and preferably occur asfollows: dip, raise, “minor” dip, dispense foam, recoat, range find,fine adjustment, exposure, and then repeat. The minor dip in particularis used to drop the surface of a last layer down so that a new layer canbe made on top of it (and not necessarily to add additional resin to thebuild surface). The dispense foam operation is described above, and itadds new material to the top of the build surface for the new layer.Preferably, the above-described operations are carried out under programcontrol, namely, computer program instructions executed by a hardwareprocessor, by firmware, by programmable logic control (PLC), or thelike.

In the example embodiment depicted above, the SLA apparatus may be aconventional SLA machine that is retrofitted (e.g., at its location ofuse) to include the associated mechanism 305. In this example, theliquid resin supplied to the pressure vessel is the conventional resinthat otherwise is held within the tank. In an alternative embodiment,and presuming sufficient stability of the foam, the tank 304 may includejust bulk foam in lieu of any liquid resin, or the tank may be partiallyfilled with bulk foam (atop the liquid resin). Another alternative issaturate the liquid in the tank with a gas and then agitate thesaturated resin (e.g., using ultrasound, mechanical agitation, etc.) toforce the foam bubbles to rise to the surface layer being printed. Thisoperation may be carried out continuously, or just before a particularlayer is printed. As the tank level falls, additional liquid resin isadded for replenishment or a suitable ballast is used to adjust thelevel of the tank.

In an alternative to the “retrofit” embodiment, the SLA apparatusincludes the foaming mechanism as original equipment, namely, as anintegral component or element.

In the embodiment described above, typically the resin applied to thepressure vessel is liquid photopolymer, such as CPS-1035F, a proprietaryresin formulation from Colorado Photopolymer Solutions (CPS).Alternative resins include, without limitation, CPS SM1035 (athiol-based resin), SM442 (a durable PDMS-like resin), and SM472 (anABS-like resin).

As used herein, and as depicted in FIG. 3, the foam delivered to thebuild plate is sometimes referred to as “radcure” foam, meaning that thematerial is radiation-curable, and wherein the type of radiation mayvary, e.g., ultraviolet (UV), visible, electron beam, and x-ray. Theterm “resin” refers to a photosensitized mixture of monomers, oligomers,and polymers that is cured by radiation. 3D printing refers to a form ofadditive manufacturing where components are made by the layer-wiseaddition of cross-sectional areas. SLA, as noted above, refers to theknown technique of stereolithography, which is a form of 3D printingwhere—according to this disclosure—radcure resins are exposed toradiation to convert a liquid polymer to a solid polymer. Laser-basedSLA uses point-to-point solidification procedure, whereas DLP-based SLAuses digital light processing to project an entire cross sectional areato form layer-wise addition. Either approach may be used herein.Subsequent layers are built up to form a product.

According to another aspect of this disclosure, the foam provided to thebuild plate may comprise the radiation-curable resin, and othermaterials. Thus, for example, the build technique herein may use astable foam comprising a suitable surfactant, particle stabilizer oremulsifier, and the radiation-curable resin. Upon frothing, e.g.,through mechanical mixing, shaking, gas injection, ultrasonicstimulation, or otherwise, a stable foam is produced. The foam is deemedstable, for example, when self-destructive processes due to liquiddrainage, ripening and coalescence are controlled. Stable foams forradiation-curable resins are well-known in the prior art. When the foamis exposed to suitable radiation (e.g., during the build process) toinitiate a polymerization reaction, it solidifies into cured resin ashas been described. Advantageously, the cured resin has a higherfraction of gas, and thus it is lighter in weight than a curednon-foamed resin. As a result, parts formed at least in part using thecured foam-based resin are lighter in weight as compared to thoseproduced using liquid resin. Further, by using radcure foam, parts areproduced more cheaply because less material is required for fabrication(due to the volume fraction occupied by the gas phase of the foam).Producing structures at least in part out of radcure foam alleviatesadditional shortcomings in the current state-of-the-art for 3D printing,such as curling and shrinking of solid objects, and in particular byincorporating internal isotropic structures. To optimize designs,comprehensive iterative computational design may also be leveraged.

In an embodiment, a radiation curable (radcure) foam concentrate C isformed by mixing a radiation curable resin A, and a foaming agent B. Arepresentative but non-limiting radiation curable resin A is PR48 fromAutodesk Ember, which is a clear resin that consists of a monomer or anoligomer (e.g., Allnex Ebecryl 8219 39.776% and Sartomer SR494 39,776%),a reactive diluent (Rahn Genomer 1122, 19.888%), a photoinitiator(Esstech TPO+ (2,4,6-Trimethylbenzoyl-diphenylphosphineoxide) 0.400%),and a UV blocker (Mayzo OB+(2,5-thiophenediyl)bis(5-6tertbutylbenzoxazole)) 0.160%. As is wellknown, resin cures by radiation-initiated free radical or cationicpolymerization mechanisms. A representative but non-limiting foamingagent is an emulsifier, surfactant, particle solid that promotes theformation and stabilization of aqueous, non-aqueous or an emulsion-basedfoam. Examples include, without limitation, diglycerol α-monomyristate(C₁₄G₂), diglycerol α-monolaurate (C₁₂G₂), glycerol α-monolaurate(C₁₂G₁), and the like. The foam C preferably is a mixture of radcureresin A and the suitable foaming agent B (surfactant, emulsifier,particle-stabilized, or the like), which is used to enhance andstabilize the foam. Typically, C is in concentrated form before beingagitated.

In an alternative embodiment, the concentrate (such as described above)is subject to frothing (e.g., agitation, mixing, shaking, gas injection,ultrasonic stimulation, combinations thereof, or the like) to produce afoam radcure resin C* in which the radcure resin and foaming agentmixture expands in volume and produces a stable non-aqueousradiation-curable foam. The foam C* may be wet or dry, with the wet foamcharacterized by spherical bubbles, and the dry foam characterized bypolyhedra.

The following describes one embodiment for making the foam C*. In thisembodiment, the foam concentrate is made by mixing a radcure resin A(90-99.5% by weight) with a foaming agent (0.5-10% by weight), whereinthe foaming agent is an emulsifier, surfactant or solid particles. Inthis embodiment, enhanced frothing and stabilized froth prior to andduring radiation curing is achieved by exemplary surfactants such as,without limitation, alkylaryl polyether alcohols, dioctyl sodiumsulfosuccinate, silicone fluids, and the like, as well as surfactantsand emulsifiers such as monoglycerols, polyglycerols, and the like, aswell as solid particles.

The concentrations of A+B to make C may vary, for example, 5-80 parts byweight of the oligomer, preferably 15-40 parts of the reactive diluent,0.05-10 parts (preferably 0.01-0.5 parts) photosensitizer; 5-30 parts(preferably 15-25 parts) plasticizer, and 0.5-10 parts (preferably 3-5parts) of the foaming agent.

As noted above, foam formation (of C into C*) preferably is achieved bymeans of gas injection, agitation, mixing, or the like. Simple shaking,mechanical mixing or frothing by a specialized frothing apparatus (e.g.,available commercially by the Oakes Company of iSi North America) can beused to generate the foam. The chemical structure of the resin andfoaming agent (e.g., polarity, functionality, molecular weight,viscosity, etc.) and foam formation mechanism (e.g., gas injection,agitation, etc.) determine the foam characteristics and structure, andthey can be tuned to generate a foam with the characteristics ofinterest (namely, uniform foam bubbles approximately 20 microns insize). Preferably, chemical liberation of gas is not advised, and careshould be taken to avoid mixing oxygen with the resin foam, as oxygen isa known reaction inhibitor for free-radical initiated reactions.

The following describes the structural attributes of C and C*. Uncuredfoams have a closed cellular structure. Stable foams are notself-destructive, e.g., due to liquid drainage, ripening, coalescence,or otherwise. They may be stable for long periods of time. Foams may bewet and characterized by regular spherical bubbles, or dry characterizedby polyhedral. With respect to their functional attributes, stable foamsexpand to occupy multiple times the volume of unfoamed liquid. Duringthe SLA build process, and according to this disclosure, theselightweight, ordered cellular structures (foam bubbles or polyhedral)solidify using radiation to produce lightweight parts from a relativelysmall volume of liquid (that comprises the foam). Stable foams of thistype cure faster than non-foamed liquid resins, and they should reduceshrinkage and curling associated with traditional radiation-curable 3Dprinted part production.

The foam C* is useful to produce any number and type of 3D parts(structures 110 or 210 in FIG. 1 and FIG. 2) during the SLA additivemanufacturing process by layer-wise additional of cross-sectional areasusing known 3D printer technologies, products and systems. The approachmay be carried out either in a top-down manner, or a bottom-up manner,or using other techniques such as continuous extrusion. A 3D partmanufactured in this manner may be identified by the uniform ornon-uniform (in cross-section) microscopic foam structure, its highdegree of polymer cross-linking, and segmentation, layers or seamsassociated with layer-wise additive manufacturing. As noted above, thestructural properties of the part are dependent on the materials used(e.g., flexible versus rigid resin), as well as on the underlyingstructure of the material.

As an alternative, and prior to printing, C (the radcure foamconcentrate) may be modified with additional components D, such asfibrous reinforcement materials (e.g., carbon fiber, fiberglass, andother organic and non-organic materials. D may range in size fromseveral microns or smaller (e.g., carbon nanotubes), to 10-100centimeters or more. When C and D are combined, the result is afiber-reinforced radcure resin. When C is agitated to C* using themethods described above, and when C contains D, the result is afiber-reinforced foamed composite resin. Radiation-curedfiber-reinforced composite materials may require additional curingenergy during manufacture because the black carbon fibers absorb UV andvisible radiation. Higher energy radiation (e.g., electron beam, x-raycuring, etc.) may be used to facilitate printing in these circumstances.

The techniques herein (using C or C*) enable large format production ofparts, at least in part because less material is required forfabrication due to the high volume fraction occupied by the gas phase.Producing structures out of radcure foam as described herein alleviatesother shortcomings of traditional 3D printing, such as part curling andshrinking. The approach herein facilitates manufacture of lighter weightparts and thus lighter-weight vehicles and the like (that include them),thereby resulting in lower emissions, lower operating expenses, and thelike. In-situ fabrication of parts using the radcure foam reducesmanufacturing costs and provides improved thermoset parts and compositesthat do not rust or corrode.

A representative 3D printer that may be used for additive manufacturingaccording to this disclosure is the Octave Light R1 70 μm printer,available from Octave Light. This is a top-down device that has a buildvolume of 204 mm (height) by 134.4 mm (width) by 75.6 mm (length), and ahorizontal XY plane resolution of 70 μm by 70 μm per pixel, and avertical Z direction resolution of 5 μm. Typically, the build layercapability is 25 μm by 125 μm. The light source is a 405 nm wavelengthUV LED, which is driven by a high precision UV DLP optical system with1920×1080 square pixels. The optical engine includes a light sensor toaccurately adjust the intensity of the UV LED. The printer includes alaser measurement sensor with 3 μm resolution that is able to measurethe surface location of the material. As noted, the build system istop-down with a recoater blade.

Experimental Data

As described above, one preferred printing technique involves“on-demand” generation of the foam layer (at the print interface). Toestablish that items could be 3D printed using foam resin and in thison-demand manner,_an experiment was performed to compare parts made, onthe one hand, from foamed radiation curable resin, and, on the otherhand, those may from conventional (i.e., unfoamed) liquid resin. Thisexperiment was carried out using an Octave Light R1 70 μm printer,available from Octave Light. This is a top-down device that has a buildvolume of 204 mm (height) by 134.4 mm (width) by 75.6 mm (length), and ahorizontal XY plane resolution of 70 μm by 70 μm per pixel, and avertical Z direction resolution of 5 μm. Typically, the build layercapability is 25 μm by 125 μm. The light source is a 405 nm wavelengthUV LED, which is driven by a high precision UV DLP optical system with1920×1080 square pixels. The optical engine includes a light sensor toaccurately adjust the intensity of the UV LED. The printer includes alaser measurement sensor with 3 μm resolution that is able to measurethe surface location of the material. The build system is top-down witha recoater blade.

The experiment involved creating six (6) cylinders, each measuring 2 mmhigh and 20 mm in diameter. A commercially-available resin, CPS-1035F,from Colorado Photopolymer Solutions, was utilized. After the build wascompleted, the samples were cleaned in an isopropyl alcohol bath for 30minutes and then post-cured under a 30 Watt UV LED flood lamp for 60minutes. The samples were then weighed on an electronic scale, and theweights were recorded with three significant figures. Samples were thencut, and cross-sectional images were obtained with a SmartZoom 5 opticalmicroscope, available from Zeiss.

The experiment was performed for the following layer thicknesses (inμm): 500, 250, 175, 150 and 125. A single control experiment wasperformed using the standard printer settings and protocol for thisresin for each of the layer thicknesses. Next, two (2) trials wereperformed using foamed resin for each layer thickness. In particular,the foam was generated using the 1035F resin and N₂O gas using as an 0.5liter whip creamer (from iSi North America). The resin was added to thewhip creamer and the lid attached. Next, a gas charge was added to thewhip creamer and the mixture was shaken thoroughly for sixty (60)seconds. The printer settings were then modified to reduce the dip depthto 10 μm (“minor dip”) to eliminate the plate dipping into the resinvat, and to reduce the speed of the recoater blade. The foam wasdispensed directly onto the build surface using the whip creamer, usinga 3 mm decorating tip nozzle. The recoater blade then spread the foamevenly onto the build surface and the light engine then displayed theappropriate image to solidify the foam.

The results of the experiment showed that the control samples were clearand the foamed samples were translucent. Under the microscope, bubbleswere clearly seen in the cross-sections of the foam samples. Thesebubbles formed lenticular structures that scattered the light, hence thetranslucent appearance. The mass of the samples also confirmed that foamwas successfully printed. All foamed samples showed a reduction in mass.The 125 um and 150 um layer size experiments show excellent uniformityacross all 12 samples, and a weight reduction of 20-25% compared to thecontrol samples.

FIG. 4 depicts a cross-section of a control sample printed in theconventional manner using a liquid resin. FIG. 5 depicts a cross-sectionof a sample (shown under normal light) printed using foam. FIG. 6depicts a cross-section of the same foam-printed sample, but shown underconfocal light. FIG. 7 depicts a chart that, for each of the layer sizestested, compares relative percentages of gas and solid volume fractionsin the resulting samples.

While the above describes a particular order of operations performed bycertain embodiments of the described subject matter, it should beunderstood that such order is exemplary, as alternative embodiments mayperform the operations in a different order, combine certain operations,overlap certain operations, or the like. References in the specificationto a given embodiment indicate that the embodiment described may includea particular feature, structure, or characteristic, but every embodimentmay not necessarily include the particular feature, structure, orcharacteristic.

While the disclosed subject matter has been described in the context ofa method or process, the subject matter also relates to apparatus forperforming the operations herein. This apparatus may be a particular 3Dprinting machine or system that is specially constructed for therequired purposes, or an existing commercial 3D printer that has beenadapted to print using the above-described foam and foam dispensingmechanism.

While the preferred technique as described above uses layer-wiseadditive manufacturing, other manufacturing processes may be used toprocess the foam to produce the build item. Thus, for example, in analternative embodiment, the radiation-curable foam is placed in a moldand exposed to an electron beam or x-ray, and the foam is then cured inthe mold. Still another alternative is to use laser holography, whereintwo lasers intersect in a tank of foamed resin and cure the resin atthat spot.

What is claimed is as follows:
 1. A method of manufacturing, comprising:processing radiation-curable resin that is in a liquid phase to producea radiation-curable foam; depositing the radiation-curable foam at acurrent build layer of a build surface; and following deposition, curingthe radiation-curable foam at the current build layer to create a layerof a three-dimensional (3D) build item.
 2. The method as described inclaim 1 wherein the radiation-curable foam is deposited on-demand justas the current build layer of the 3D build item is about to be printed.3. The method as described in claim 1 further including repeating thedepositing and printing operations to create one or more additionallayers of the 3D build item.
 4. The method as described in claim 1wherein the processing is one of: agitation, mixing, shaking, gasinjection, ultrasonic stimulation, and combinations thereof.
 5. Themethod as described in claim 1 wherein, prior to the depositing, themethod further includes mixing the radiation-cured resin and a foamingagent to produce a concentrate.
 6. The method as described in claim 5wherein the foaming agent is one of: an emulsifier, a surfactant, aparticle solid, and combinations thereof.
 7. The method as described inclaim 6 wherein the mixture is 90-99% by weight of the radiation-curedresin, and 0.5-10% by weight of the foaming agent.
 8. The method asdescribed in claim 5 wherein the concentrate further comprises areinforcing material.
 9. A method of manufacturing in association with aradiation source, a tank normally configured to hold photopolymer resin,and a build plate configured to move within the tank, comprising:producing and depositing on-demand a radiation-curable foam at a currentbuild layer of a build surface, the radiation-curable foam produced froma liquid photopolymer; following deposition, curing theradiation-curable foam at the current build layer to create a layer of athree-dimensional (3D) build item; and repeating the producing,depositing and curing steps to create one or more additional layers ofthe 3D build item.
 10. The method as described in claim 9 wherein theradiation-curable foam is produced externally to the tank and suppliedto the build surface.
 11. The method as described in claim 10 whereinthe radiation-curable foam is produced by dissolving a gas in a vesselcontaining the liquid resin, and delivering the gas and liquid resinmixture under pressure to the build plate.
 12. The method as describedin claim 9 wherein the radiation-curable foam is produced in associationwith the liquid resin in the tank.
 13. The method as described in claim12 wherein the radiation-curable foam is produced by dissolving a gas inthe liquid resin in the tank, and agitating the gas and liquid resinmixture.
 14. A three-dimensional (3D) article of manufacture madeaccording to a layer-wise additive manufacturing process, comprising:processing radiation-curable resin that is in a liquid phase to producea radiation-curable foam; depositing the radiation-curable foam at acurrent build layer of a build surface; and following deposition, curingthe non-aqueous radiation-curable foam at the current build layer tocreate a layer of the three-dimensional (3D) build item.
 15. The articleof manufacture as described in claim 14 wherein, according to theprocess, the radiation-curable foam is deposited on-demand just as thecurrent build layer of the 3D build item is about to be printed.
 16. Thearticle of manufacture as described in claim 14 wherein the processfurther includes repeating the depositing and printing operations tocreate one or more additional layers of the 3D build item.
 17. Thearticle of manufacture as described in claim 14 wherein, according tothe process, the processing is one of: agitation, mixing, shaking, gasinjection, ultrasonic stimulation, and combinations thereof.